Composite materials using microfibers of cellulose have recently been investigated enthusiastically. It is known that cellulose exhibits a low coefficient of linear expansion, a high modulus of elasticity, and a high strength due to the extended chain crystals thereof. In addition, cellulose has attracted an attention as a material that exhibits high transparency when microfibrillated to give a composite material.
For example, PTL 1 discloses a method for preparing microfibrillated cellulose fibers by subjecting cellulose fiber raw materials composed of purification-treated wood flour to a fibrillation treatment using an ultrahigh pressure homogenizer. Further, PTL 2 discloses a method for preparing microfibrillated cellulose fibers by carrying out a fibrillation treatment using an ultrasonic irradiation apparatus.